Constant tension line-tensioning mechanism

ABSTRACT

Constant line tension can be maintained in a ship&#39;&#39;s mooring or towing line extending from a winch by supplying to a polyphase phase-wound induction motor driving the winch alternating current from an alternating-current source the frequency of which is variable in response to the load on the winch. Such variablefrequency source may be an alternator driven by a phase-wound induction machine powered to operate as a motor. The variablefrequency AC source is connected to the winch motor to drive the winch only in the reeling-in direction, but the tension on the line can retard the motor speed or stall the motor or rotate the winch and motor in the opposite, paying-out direction against the reeling-in driving torque of the motor. The winch motor torque can be adjusted by varying the value of resistance shunted across the rotor winding of the winch motor. The line can be retrieved very quickly by having a squirrel-cage alternating-current motor connected mechanically to the phase-wound induction machine. During constant-line-tension operation, such motor is simply idly rotated with such machine, but for rapid line retrieval the motor can be powered by the same AC supply as powers the phase-wound induction machine and such motor will then drive the phase-wound induction machine positively. The winch-motor torque can be adjusted by varying the value of resistance shunted across the rotor winding of the winch motor. Also, for towing applications the voltage of the variable-frequency source can be altered in response to variations in the length of line paid out or reeled in to control the winch motor in turn in response to sensing the extent of rotation of the winch drum in paying out or reeling in the towing line and correspondingly varying the field excitation of the alternating-current generator supplying current to the winch motor to operate the winch motor for restoring the line to its original length.

United States Patent 1191 Ostrom CONSTANT TENSION LINE-TENSIONINGMECHANISM [75] Inventor: Cyrus W. Ostrom, Seattle, Wash.

[73] Assignee: Consolidated Electric Corporation,

Seattle, Wash.

[ Notice: The portion of the'term of this patent subsequent to Jan. 14,1986, has been disclaimed.

[22] Filed: Apr. 23, 1973 [21] App]. No.: 353,654

Related US Application Data abandoned.

[52] US. Cl. 25d/T72Y318/6 [51] Int. Cl B66d 1/48 [58] Field of Search254/172, 173 R, 173 B,

[56] References Cited UNITED STATES PATENTS 1,551,419 8/1925 Merrill254/172 3,421,736 l/l969 Ostrom 254/172 Primary Examiner-James B.Marbert Assistant Examiner-James L. Rowland Attorney, Agent, orFirmRobert W. Beach [57] ABSTRACT Constant line tension can bemaintained in a ships mooring or towing line extending from a winch bysupplying to a polyphase phase-wound induction motor driving the winchalternating current from an alternating-current source the frequency ofwhich is variable in response to the load on the winch. Suchvariable-frequency source may be an alternator driven by a phase-woundinduction machine powered to operate as a motor. The variable-frequencyAC source is connected to the winch motor to drive the winch only in thereeling-in direction, but the tension on the line can retard the motorspeed or stall the motor or rotate the winch and motor in the opposite,paying-out direction against the reeling-in driving torque of the motor.The winch motor torque can be adjusted by varying the value ofresistance shunted across the rotor winding of the winch motor. The linecan be retrieved very quickly by having a squirrel-cagealternating-current motor connected mechanically to the phase-woundinduction machine. During constant-line-tension operation, such motor issimply idly rotated with such machine, but for rapid line retrieval themotor can be powered by the same AC supply as powers the phasewoundinduction machine and such motor will then drive the phase-woundinduction machine positively. The winch-motor torque can be adjusted byvarying the value of resistance shunted across the rotor winding of thewinch motor. Also, for towing applications the voltage of thevariable-frequency source can be altered in response to variations inthe length of line paid out or reeled in to control the winch motor inturn in response to sensing the extent of rotation of the winch drum inpaying out or reeling in the towing line and correspondingly varying thefield excitation of the alternating-current generator supplying currentto the winch motor to operate the winch motor for restoring the line toits original length.

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CYRUS M OSTFFOM 14 TTORNE Y CONSTANT TENSION LlNE-TENSIONING MECHANISMThis is a continuation of application Ser. No. 099,575, filed Dec. 18,1970 now abandoned.

This invention relates to the general type of continual tensionline-tensioning mechanism disclosed in US. Pat. No. 3,42l,736, and thegeneral purpose of the present invention is to make mechanism of thattype more useful and versatile.

Especially it is an object of the present invention to enable mechanismof the general type disclosed in said US. Pat. No. 3,421,736 to beutilized for maintaining a substantially constant tension in a lineconnecting a tug and its tow as an operation alternative to using suchmechanism for maintaining a substantially constant tension in a shipsmooring line.

Particularly when the mechanism is used in connection with a line formooring a ship, but alsowhen it is used in connection with a line fortowing, it is an object to be able to override the automatictension-control mechanism andto reel in line very rapidly when it hasbeen cast off.

Principally when the mechanism is used for maintaining a constanttension in a towing line itis an object to be able to override theconstant tension mechanism and limit the extent to which the lineisreele'd in or paid out from a reference length irrespective of thetension in the line.

An additional object is to be able to regulate at will the degree ofvariation in length of towing line which will be permitted by themechanism.

FIG. 1 is a diagrammatic top perspective of the bow portion of a shipand a dock portion to which the ship is moored in conjunction with thewiring diagram of a ship winch drive motor and a regulated power supplyfor such motor.

FIG. 2 is a diagrammatic top perspective of the stern portion of a tugand the bow portion of a barge tow interconnected by a towing line inconjunction with a wiring diagram of a ship winch drive motor.

FIG. 3 is a wiring diagram of a power supply for the winch-driving motorof FIG. 2.

FIG. 4 is a diagram showing the relationship of and connections betweenvarious components of the mechanism including the winch, power supplyfor the winch and control mechanism for such power supply.

The mechanism illustrated in the drawings exerts on a line, such as amooring line or a towing line of a ship, a selected substantiallyconstant line tension. Such linehauling mechanism can be controlled sothat the tension on the line can be alerted at will to reel in or payout the line and the speed of operation or torque of the line-windingmeans can be altered at will. This invention has particularlyadvantageous application to the winch of a ship mooring line or towingline and, consequcntly, the invention will be described with referenceto these applications, although it will be understood that suchmechanism can be used in any type of installation in which it is desiredto maintain a substantially constant line tension where the variation inlength of the line is limited.

In FIG. 1 of the drawings the foredeck of a ship 1 is illustrated fromwhich a line 2 extends to a bollard 3 on a dock. The line 2 is tensionedby line-winding means, illustrated as a deck winch 4 to which a winchmotor 5 is connected. When the winch motor is not in operation, thewinch drum is secured against rotation by brake 6 as indicated in FIG.4. Such brake can be of the drum and band type in which the brake bandis held in position clamping the brake drum by compression spring means.The clamping action of the brake drum is released automatically by anelectric solenoid connected in circuit with the winch motor 5 so thatwhen the winch motor is energized the brake solenoid will be energizedsimultaneously to release the braking action. Correspondingly, when thewinch driving motor is deenergized the brake-releasing solenoid will bedeenergized so that the brake band will be clamped by its spring to thebrake drum so to secure the winch drum against rotation.

The winch motor 5 is of the polyphase phase-wound induction type,including a three-phase Y-connected stator winding 7. During a mooringoperation this winding can be connected to a constant frequency ACsource 8, which may be the ship AC supply. Such supply may, for example,be of the three-phase 60 cyclesper-second type having 440 voltage. SuchAC source can be connected through a starting switch 9 in such phaserelationship to the stator winding 7 as to energize the motor to turn inthe direction for driving the winch drum 4 to reel in the mooring line.Conversely, the such source can be connected in a different phaserelationship through reversing switch 10 to the stator winding 7 of themotor so as to cause the rotor of the motor to turn in a direction suchthat the winch drum 4 pays out mooring line 2.

While the starting switches 9 and 10 determine in which direction thewinch motor 5 and the drum of winch 4 will turn, the speed and torque ofthe motor in either direction will be determined by the manner in whichthe phase-wound coils of the rotor 11 are connected together. Such rotorwindings are interconnected by wires 12, but such wires include in themslide-wire resistances 12 which can be bridged at different locations bya set of interconnected adjustable brushes 12". These brushes can bemoved conjointly along the slide wires 12 in corresponding positions, orthe connections to the resistances can be in the form of taps andconnectors can connect together corresponding taps of the respectiveresistances 12' to provide an equivalent variation in resistance value.

To operate the winch 4 in a normal operation effecting mooring of aship, therefore, the switch 9 can be closed to energize the motor 5 forreeling in the mooring line 2 or the switch 10 can be closed to energizethe motor 5 for driving the winch 4 to pay out the line 2 and thebridging connections 12" can be set to decrease the effective resistancein the rotor connections for increasing the speed and/or torque of themotor to any desired value within the capability of the motor. When theship has been brought into its desired mooring position the switches 9and 10 are opened and the switch 9 is closed to connect the statorwinding 7 of the winch motor 5 continuously to a load-responsivevariable-frequency AC source 8 instead of to the constant-frequency ACsource 8 to which the motor was connected by the switch 9 or the switch10, to provide the desired operation for maintaining a substantiallyconstant line tension.

The winding 7 of the winch motor 5 can be connected to thevariable-frequency AC source 8 only by the switch 9 representingrotation of the motor and winch 4 in a reeling-in direction. Morespecifically, the motor cannot be connected to the variable-frequency ACsource in a direction to pay out line, although, as will be discussedhereinafter, if sufficient tension is exerted on the line 2 the winch 4and winch motor 5 not only can be stopped but can be turned by the linetension in a reverse or overhauling direction to enable line to beunreeled from the drum of winch 4 even though torque is being appliedcontinuously to that drum by the motor 5 tending to reel in the line.

Whether the motor 5, when the switch 9 is closed, will turn winch 4 in adirection to reel in line 2, or will be stopped, or actually will beturned reversely so that winch 4 will pay out line 2, depends upon thedegree of torque exerted by the motor on the winch drum. Such torque, inturn, depends upon the power consumed by the motor and the amount ofpower consumed is governed by the amount of resistance 12 in theconnections between the coils of the rotor 11. The greater the amount ofresistance the less current will flow, the less will be the powerabsorbed by the motor and the smaller will be the torque developed bythe motor.

As in the operation of the motor 5 when it is cnnected to theconstant-frequency AC supply 8, it is also desirable to be able to alterthe amount of resistance in the connections of rotor 11 when the motoris connected to the variable-frequency AC source 8. The sameresistance-adjusting mechanism can be used for altering the amount ofthe resistances 12 between the rotor coils 11 and the bridging wires 12"when current is supplied to the motor from the source 8. Altering theamount of effective resistance in the connections between the rotorwindings will, however, not have as great an effect on the torqueexerted by the winch motor when it is connected to thevariable-frequency AC source 8' as when the motor is connected to theconstant-frequency source 8 because the power consumed by the motordepends not only on the resistance in the rotor circuit, but also on thefrequency and voltage applied to the stator winding 7.

As indicated in FIG. 1, it is desirable for the frequency of the ACsource 8 to be variable in response to the mechanical torque load on themotor 5, which is reflected in the current supplied to the statorwindings 7. As the mechanical torque load on the motor increases and thestator current increases, it is desirable for the frequency of thecurrent supplied to the motor to drop so as to enable the motor to havethe type of operating characteristics desired, namely, characteristicsof high torque but low speed. Consequently, it is preferred that themaximum frequency of the variablefrequency source 8 be considerablylower than the frequency of the constant-frequency source 8. Instead ofbeing 60 cycles per second, therefore, the maximum frequency of thesource 8 can, for example, be half that value, namely, 30 cycles persecond. As the mechanical torque load increases on the mooring winch andmotor, the frequency can be reduced progressively with increase in loadto a value in the range of 15 to cycles and the input voltage can dropfrom 220 volts to I20 or 130 volts, for example, while the currentincreases.

While the load-responsive variable-frequency AC source 8 can be ofvarious types, FIG. 1 illustrates such a power source which has provento be quite satisfactory. Such source is a motor-generator set,including a polyphase phase-wound induction machine powered to operateas a motor 13 connected to drive an alternator 14. The stator windings15 of such motor can be connected by a switch 16 to the ship powersupply 8, such as three-phase -cycle current having 440 voltage. Thecoils of rotor 17 are interconnected through switch 36 by wires 18having in them resistances 18'. The degree of effective resistance be beselected or adjusted for calibration purposes by bridging wires 18"which can be set so that under no load the alternator 14 will be turnedat the speed of 600 rpm. to produce 30- cycle alternating current.

The coils of the alternator rotor 19 must be excited so as to magnetizethe rotor for developing electricity in the stator windings 20 connectedto the output line 21. Excitation current is supplied to the coils ofthe alternator rotor 19 from a DC source 22 which. come niently, may berectified AC. Increase in electrical loading of the alternator reflectedby an increase in current passing through the output leads 2] to thewinch motor 11, because of the increase in mechanical torque load onsuch motor and the winch 4, will tend to reduce the speed of thealternator. Reduction in speed of the alternator would result in adecrease in output voltage and a reduction in frequency. The reductionin frequency would correspond directly to the reduction in alternatorrotor speed.

An increase in load on mooring line 2 resulting from a tendency of theship to move away from the mooring bollard 3 increases the mechanicaltorque load on the winch 4 and winch motor 5 so as to increase thedemand for current flowing through the stator coils of such motor whichare continuously connected to the variable-frequency AC source 8 whilethe ship is being maintained in moored condition. Such increase incurrent must be supplied from the output loads connected to the statorwindings 20 of alternator 14 so as to increase the electric power loadon the alternator. As such output current load increases, it isdesirable for the output frequency of alternator 14 to decrease, whichcan only result from a decrease in alternator speed. Such decrease inalternator speed can only result from a decrease in speed of the motordriving the alternator which, in the case of FIG. I, is the motor 13,caused by an increase in the mechanical torque load on such motorresulting from the increased electrical load on the alternator 14 towhich it is drivingly connected.

A characteristic of a polyphase phase-wound induction motor is that itsspeed is reduced as the mechanical torque load on it is increased and,consequently, such a motor is suitable for driving the alternator 14 tomaintain a substantially constant tension on the winch line when suchline is attached to the bollard 3 or other object. When the line is castoff, however, it is desirable to be able to increase the speed of thewinch motor 5 and the winch 4 to reel in the slack line very quickly toprevent the trailing line from being fouled in propellers or bowthrusters or from becoming snagged. The pres ent invention provides anarrangement which will enable motor 5 to be rotated in a reeling-indirection at approximately twice the speed that such motor would turn ifits field 7 were connected directly to the 440- volt power supply line 8by opening switch 9 and closing switch 9.

The mechanism to accomplish such high-speed reeling in rotation of winchmotor 7 includes an alternating current three-phase squirrel cageinduction motor 34, having its shaft permanently connected to the shaftof rotor 17 of the polyphase phase-wound induction motor 13. The statorof motor 34 can be connected to the 440-volt, 60-cycle supply line 8 bya three-pole The key to the high-speed drive of winch motor 5 resides inthe two factors that, first the speed of the polyphase, phase-woundinduction-type motor 5 varies generally'in proportion to the frequencyof the alternating current supplied to it for a given voltage, and,second, the polyphase phase-wound induction machine 13 is capable ofbeing supplied with electricity to operate as a motor and,alternatively, is capable of being driven mechanically to operate as analternator.

During constant-tension operation of the system, as has been explainedabove, the switch 16 will be closed to supply 60-cycle alternatingcurrent from the supply line 8 to the stator winding of the electricalmachine 13, so as to drive its rotor 17 electrically as a motor forturning the rotor 19 of alternator 14. Such rotation of the alternatorrotor will effect generation of alternating current in the field winding20, which will be supplied through'the closed switch 9' to the fieldwinding 7 of the winch motor 5. During such operation rotation of therotor 17 will correspondingly rotate the rotor of motor 34 undervirtually no load.

When it is desired to convert the operation of motor 5 from aconstant-tension operation to a high-speed reeling-in operation, switch16 is opened to deenergize motor 13 and switch 9' is opened to removeall electrical load from the alternator 14, so that its rotor 19 can beturned idly conjointly with rotor 17 of machine 13. Switch 36 is thenopened, and switch 38 is closed to connect leads 39 and 40 together, sothat the stator winding 7 of motor 5 is substituted for the resistiveload 18 on the windings of rotor 17. Under these conditions no power issupplied to the winch motor 5.

Closing of the switch 16 would tend to turn rotor 17 in the clockwisedirection indicated by the arrow. Closing of reversing switch 37, on theother hand, would tend to turn the rotor 17 in the opposite orcounterclockwise direction. If switch 35 is closed at the same time,however, the squirrel-cage motor 34 will actually effect rotation ofrotor 17 of electrical machine 13 in the clockwise direction.

While a squirrel-cage induction motor is not a synchronous motor, it isvirtually a constant-speed motor in that its speed is reduced onlyslightly at full load over its speed under no load. Consequently, theelectrical field in the stator winding 15 of the electrical machine 13is rotating in a counterclockwise direction at approximately the samespeed that the rotor windings 17 are being rotated mechanically in theclockwise direction. Since both of these rotations are the result of 60-cycle alternating current input, current will be generated in thewindings of the rotor 17 at a frequency equal to the algebraic sum ofthe rotating electrical field and the rotating rotor windings, orapproximately 120 cycles. By impressing the l-cycle alternating currentgenerated by the windings of rotor 17 onto the stator windings 7 of themotor 5, such motor will rotate in the reeling-in direction atapproximately twice the speed at which it would rotate if switch 38 wereopen and switch 9 were closed, connecting the stator directly to tneship supply line 8.

To accomplish the generation of alternating current at double frequencyby the windings of rotor 17, it is necessary for the induction motor 34and the electrical machine 13 to be matched eo that the nominal speed ofthe induction motor is approximately equal to the synchronous speed atwhich the rotor 17 would be turned in the clockwise direction if switch16 were closed, or in the counterclockwise direction if switch 37 wereclosed. A representative speed would be 900 rpm. It will be noted thatit is necessary to stop the electrical machine 13 in order to convertfrom the constant-tension type of operation to the high-speed reeling-inoperation if the switch 35 is closed before the switch 16 is opened andthe switch 37 is closed.

For constant line tension operation the rotor 17 of the electricalmachine 13 would be rotating in the clockwise direction the same as itwould be rotating when driven by motor 34 during high-speed reeling-in.Consequently, there would be no appreciable mechanical shock in changingfrom one type of operation to the other. Also, torque is applied to thewinch motor winding 7 in the reeling-in direction under constant-tensionoperation, so, if the line 2 were cast off, the motor 5 would begin topick up speed in the reeling-in direction. Substitution of powergenerated by the coils of rotor 17 for power generated by the statorcoils 20 of alternator 14 would simply accelerate the winchmotor 5 tothe high-speed reeling-in condition more rapidly, because the motorwould be operating under light load.

With the mechanism illustrated in FIG. 1, therefore, a choice of fourtypes of operation is available, namely, first, conventional reeling-inoperation by connecting stator windings 7 to power supply 8 by closingswitch 9; second, conventional paying-out operation by connecting statorwindings 7 to power supply 8 by closing switch 10; third,constant-tension operation by connecting stator windings 7 to thealternator 14 by closing switch 9'; and, fourth, high-speed reeling-inby connecting stator windings 7 to rotor windings 17 by closing switch38 with switches 26, 9, 9' and 10 open when such rotor is drivenpositively by the squirrel-cageinduction motor 34..

FIGS. 2 and 3 illustrate an adaptation of the same general type ofmechanism shown as being utilized on,

a tug 1' intowing a barge 1" by a line 2'. Such line is wound on a drum4' on the stern of the tug, and has a bridle connected to towing bitts3' onthe barge. The shaft of the reversible winch motor 5 is connectedto the drum 4' so that it may be turned to reel in or pay out line. Thedesired initial length of line can be selected by closing switch 9 orswitch 10 to connect the stator 7 of the motor to the supply line 8 forefi'ecting rotation of the motor in the reeling-in direction orpaying-out direction, respectively. When the desired length of towingline has been established, the switch 9 or 10 is opened, and the switch9' is closed to connect the stator coils 7 of the winch motor to theoutput lines 21 connected to the stator coils 20 of the alternator 14.By driving the rotor 19 of the alternator by the rotor 17 of thepolyphase phase-wound induction motor 13, a substantially constanttension can be maintained in the towing line 2 despite uncoordinatedpitching and heaving of the tug and barge resulting from heavy weather.

In towing operations, however, it is also desirable to maintained thelength of the towing line 2' substantially constant within reasonablelimits, although it is much more important that the tension forces inthe line be maintained substantially constant rather than the length ofthe line being kept constant. The present invention includes a provisionfor maintaining the length of the tow line constant within reasonablelimits, as well as preventing substantial fluctuations in the towlinetension. For this purpose a scope or line-length sensor 39 is connectedto the winch drum 4.

The essential component of the scope sensor 39 is a rheostat which isadjusted automatically from a selected value in response to rotation ofthe winch drum 4'. The winch drum and rheostat are connected by suitablegearing, or other suitable mechanical connection, so that as the drumturns in the reeling-in direction the resistance will be increased,whereas when the line pays out the resistance will be decreased. Thisresistance is connected by leads 42 and 43 in the circuit between themotor field 19 and the DC rotor field excitation current source 22. Inaddition, a manually adjustable rheostat 40 is connected by leads 41 and42 in series with the scope sensor rheostat 39.

When the desired length of towline 2' has been selected, the manuallyadjustable rheostat 40 is turned until the tension in towline 2' hasbeen established which will maintain the desired length of towline undersmooth towing conditions for the particular barge, barge load and towingspeed. If the weather or seas tend to separate the tug and the tow, thetowing line will lengthen. The scope sensor will be actuatedautomatically in response to paying-out rotation of the drum 4' todecrease the resistance of the rheostat 39, so that a larger excitationcurrent will flow to the rotor 19 of the alternator, causing a highervoltage output from the stator winding 20, resulting in the winch motor5 developing a greater torque without the torque of the winch and thepull on the line being decreased appreciably before such greater torqueis developed.

The greater torque applied by the winch motor 5 to the drum 4 will, ofcourse, increase the tension in towing line 2' somewhat, tending to reelthe line in. Such increase in line tension will, however, be gradual andprogressive rather than abrupt. As the line is reeled in, the rheostatof the scope sensor will be adjusted automatically to increase theresistance of the rheostat 39 again to its initial value as the towingline is restored to its original length.

Conversely, if the towing line should tend to slacken, the winch drum 4'will rotate in the reeling-in dirction which will turn the scope sensorrheostat 39 in the direction to increase the resistance in the rotorfield excitation circuit. Such increase in resistance will decrease theexcitation current, causing the output voltage from the stator windingsto be reduced. The resultant reduction in torque applied by the winchdrum motor 5 to the winch drum willenable the towing line 2' to pay outuntil the scope sensor rheostat again has been adjusted to its initialresistance value. The more the towing line varies in length, of course,the greater will be the adjustment of the scope sensor rheostat 39, andthe alteration in torque on the winding drum 4' effected by the motor 5will vary correspondingly. Consequently the greater the change in lengthof the towing line which is effected, the greater will be the alterationin tension of the towing line in a sense tending to restore the line toits original length.

In addition to adjusting the tension of towing line 2' automatically toinduce restoration of the initial towing line length, a visual oraudible alarm can be provided to be actuated by movement of the rheostat39 to increase or to decrease the resistance more than a predeterminedamount. The pilot is thus alerted to the presence of altered operatingconditions so that he can supplement the effect of the scope sensor 39by manually adjusting rheostat 40. While not shown in FIGS. 2 and 3,this system can be equipped with the high-speed reeling-in accessoryshown in FIG. 1.

While FIGS. 1, 2 and 3 show representative circuit diagrams, therelationship of physical components of the system is portrayed to betteradvantage in FIG. 4. The ships power supply 8 can be connected to a maincontrol panel 24 containing suitable fuses and, perhaps, switches 9 and10. The automatic control panel 25 may be connected to the main controlpanel which, in turn, is also connected to the winch motor 5 and thebrake 6. To such automatic control panel is connected the alternator 14by a circuit 21. The alternator drive control 26 is connected to themotor 13 and may include the switches 16 and 37. The resistance gridbank 12' for the winch motor is connected to the automatic control panel25 and the calibrating resistance grid bank 18' for the alternator drivemotor, if it is of the phasewound inductance type, is connected to thealternator drive control panel 26.

It is desirable for the winch drive motor 5 to be capable of beingcontrolled from a location remote from the control panels 24, 25 and 26.Consequently, it is desirable for such control panels to containswitch-actuating relays for the several switches 9, l0, 16, 37, 35, 9and 38 and simply to extend control circuits to a suitable controller.Such remotely located controller shown in FIG. 4 includes a handle 27for the purpose of controlling engagement of switch 9 or switch 10 andof adjusting in steps the amount of the resistances l2 effectivelyconnected to the windings of rotor 11 through the bridging circuit 12".The controller also has a handle 28 operable to control closing ofswitches 16 and 9 in sequence, or opening of switches 16, 9 and 36 andclosing of switches 35, 38 and 37 in sequence.

In use, handle 27 can be swung in one direction to close switch 9 forinitiating energization of the winch motor 5 with the maximum amount ofresistances 12 in the circuit. Continued movement of such handle in thesame direction through successive steps will reduce progressively theamount of resistance 12 effectively in the circuit of rotor 11 so as toincrease the speed or torque of the winch motor. If the handle 27 ismoved in the opposite direction past its central position, it willeffect opening of switch 9 and closing of switch 10 to effect reversalof the direction of rotation of motor 5. Continued movement of thehandle 27 in such reverse direction will progressively decrease theamount of resistance l2 effectively in the circuit of the motor rotor 11so as to increase the speed or torque of the motor.

After the handle 27 has been restored to its central off position,handle 28 can be moved into a position the handle can be moved fartherinto automatic" position. Handle 27 can then be moved into the firstposition in which the maximum resistance 12 is included in the circuitof rotor 11 of motor 5. Next the handle can be moved step-by-step intopositions in which the amount of resistance 12 in the circuit of winchmotor rotor 11 is reduced progressively by effecting shifting of thebridging connections 12".

The effect of such manipulation of the controls on the operation of thewinch 4 under automatic condi tion is that when the handle 27 is in thefirst position the winch motor 5 will drive the winch 4 to reel in lineif the line pull is less than a selected value. As the line pullincreases and the mechanical torque of winch 4 and winch motor 5increases correspondingly, the speed of the motor 5 and winch 4decreases until they are stopped at the constant tension line pull. Ifthe line pull increases beyond that value, line will be unreeled fromthe winch drum.

When the controller handle 27 is set in the second position, the sametype of operation ensues, except that the critical value of line pullwill be altered. If the tension in line 2 should decrease below thisvalue, the motor 5 will drive the winch 4 in a reeling-in directionuntil that value of line tension is reached. If the line tension shoulddecrease above that value, line will be paid out at a speed dependingupon the tension of the line until such tension has been reduced againto the critical value. If the controller is shifted to the thirdposition, the critical value of line tension will be still higher. Ifthe controller handle 27 is moved to the fourth position, the criticalvalue of line tension again will be increased. In each case, the motorand winch drum will be rotated to pay out or reel in line as may benecessary to restore the selected critical value of ,line tension forwhich the controller is set.

When the apparatus is used for towing, it will be convenient to mountthe controller for rheostat 40 on the remotely located controllerstandard as shown in FIG. 4. Such rheostat adjustment will then bereadily available to the pilot for changing the output of alternator 14to enable the length of the towing line to be increased or to decreasethe length of such line, depending upon whether the towing line hasshortened or lengthened excessively.

Even when the motor and winch are stopped, power is being consumed.Also, the higher the line pull and torque, the greater will be the loadon the variablefrequency AC source 8' and, consequently, the lower willbe the frequency and voltage. Such reduction in frequency and voltagewill, of course, be the result of the reduction in speed of the motor 13in a motoralternator type of AC source. The power consumed when thewinch motor and winch are not moving generates heat and, consequently,it may be desirable to provide suitable means for cooling the motor 5and resistance grid banks 12' and 18 and, perhaps, the motor 13 andalternator 14. Such cooling mechanism is represented by a fan 30 shownin FIG. 4 which would be energized whenever the switch 9 is closed.

The winch motor 5, alternator drive motor 13, alternator l4, and motor34 are all of standard construction, as are the switches 9, l0, 16, 35,36, 37, 38 and 9. No complex relay or circuit-breaker system isrequired, although relays to provide for remote control by the handles27 and 28 are needed and normal fuses r overlaod circuit-breakers shouldbe provided in the system, as

will be apparent to person skilled in the art. No particular toleranceor variation from a selected line tension is required to effectoperation of the system, but the system will maintain a steady pull onthe line even if no conditions occur which would alter the line pull. Ifthe line pull drops below the selected value, thus reducing the load onthe variable-frequency AC source 8, the frequency will increase, thusautomatically increasing the power available to the winch motor forexpediting winding-in rotation of the winch 4 to restore the linetension to the predetermined value. Thus, the previous condition of theline tension is restored without appreciable hunting or overtravel.

Power utilized is minimum because driving movement of equipment iseffected only as and when necessary to restore the selected linetension. Despite the tendency of the automatic system to maintain itsstability, the selected line tension can be varied easily andinstantaneously, or the automatic mechanism can be rendered inoperativeand the winch motor immediately placed under manual control to effectvoluntary rotation of the winch drum in either direction withoutreference to line pull.

I claim:

1. In line-tensioning mechanism including linewinding means connected toa towing line, an electric line-winding means motor continuouslyconnected to supply continuous mechanical torque to the linewindingmeans for winding in such line whenever the mechanical torque on theline-winding means produced by the line tension tends to drop below themechanical torque produced on the line-winding means by the line-windingmeans motor, an alternator connected to supply alternating electriccurrent to said linewinding means motor continuously for producingcontinuous mechanical torque on the line-winding means tending to reelin line whether said line-winding means motor is stopped or is turningin the line-reeling-in direction or is turned in the line-paying-outdirection by the winding means resulting from tension in the towingline, load-responsive means responsive to the electric load on saidalternator resulting from the mechanical torque produced by saidline-winding means motor on the line-winding means and operable to varyan electrical output characteristic of said alternator automatically inresponse to variation in mechanical torque exerted by said line-windingmeans motor on the linewinding means resulting from changes in towingline tension and corresponding variation in electric load on saidalternator, variable-resistance means adjustable for altering the speedof said alternator and consequently an electric output characteristic ofthe power supplied by said alternator to said line-winding means motorfor altering the torque of said motor on the linewinding means,line-length-sensing means connected to the line-winding means and tosaid variable-resistance means and always operable automatically inresponse to paying-out rotation of the line-winding means to effectadjustment of said variable-resistance means for increasing the speed ofsaid alternator and thereby increasing the torque of said line-windingmeans motor on the line-winding means and increasing the towing linetension gradually and progressively without interruption rather thanabruptly as the towing line is paid out, tending to reel in the towingline.

1. In line-tensioning mechanism including line-winding means connectedto a towing line, an electric line-winding means motor continuouslyconnected to supply continuous mechanical torque to the line-windingmeans for winding in such line whenever the mechanical torque on theline-winding means produced by the line tension tends to drop below themechanical torque produced on the line-winding means by the line-windingmeans motor, an alternator connected to supply alternating electriccurrent to said linewinding means motor continuously for producingcontinuous mechanical torque on the line-winding means tending to reelin line whether said line-winding means motor is stopped or is turningin the line-reeling-in direction or is turned in the line-paying-outdirection by the winding means resulting from tension in the towingline, load-responsive means responsive to the electric load on saidalternator resulting from the mechanical torque produced by saidline-winding means motor on the line-winding means and operable to varyan electrical output characteristic of said alternator automatically inresponse to variation in mechanical torque exerted by said line-windingmeans motor on the line-winding means resulting from changes in towingline tension and corresponding variation in electric load on saidalternator, variable-resistance means adjustable for altering the speedof said alternator and consequently an electric output characteristic ofthe power supplied by said alternator to said line-winding means motorfor altering the torque of said motor on the line-winding means,line-length-sensing means connected to the line-winding means and tosaid variable-resistance means and always operable automatically inresponse to paying-out rotation of the line-winding means to effectadjustment of said variableresistance means for increasing the speed ofsaid alternator and thereby increasing the torque of said line-windingmeans motor on the line-winding means and increasing the towing linetension gradually and progressively without interruption rather thanabruptly as the towing line is paid out, tending to reel in the towingline.